1. Field of the Invention
The present invention relates generally to the fields of chemical engineering of plated non-conductive products and methods for creating such products. More specifically, the present invention relates to plated non-conductive products used in vehicles, computer-related machines, office equipment or the like and a plating method for the same.
2. Description of the Related Art
Of non-conductive products, for instance, resin products molded by injection molding are generally subjected to surface processing to give glitter and brightness to the surface. For that purpose, a method of depositing metal on a surface of a non-conductive product in a vacuum, a method of sputtering metal, or a method of electroless plating, or the like, have been employed. In some applications, actual needs are satisfied by any of the methods described above, but in other applications, high durability of products is required, and in that case electroplating is also required.
A non-conductive product does not have conductivity, and for plating a non-conductive product, processing is required for converting a surface of the non-conductive product to a conductive one. In this case, at first, a surface of the non-conductive product is cleaned, then etched, subjected to processing such as catalyzing, and further subjected to electroless plating. This processing sequence is quite complicated.
In contrast, a method of applying a conductive paint on a surface of a non-conductive product and then subjecting the product to electroplating has been proposed. The conductive paint is generally produced by dispersing an active and conductive metallic material or a conductive organic material in a composition containing a resin vehicle, an organic solvent, a stabilizer, a dispersant, and a plasticizer or the like; and a coating film formed with the conductive paint can endure severe environmental conditions. However, if resin constituting a molded product to be painted is polypropylene (PP), polybutylene terephthalate (PBT), polyamide (PA), polycarbonate (PC), or the like, paint adheres to the surface weakly, so that there are some restrictions in selection of resin for producing molded products.
To overcome this problem, for improving adhesiveness of resin to a surface of a molded product, the so-called two-coat painting is often carried out in which polymer painting is executed to a molded product and then a conductive paint is applied to the surface. Further, with the conductive paints used currently, the adhesiveness between a conductive coating film as the foundation and a plate layer is weak, and durability of the plate layer is not sufficient. For this reason, there are some restrictions when the product subjected to the processing described above is used in a severe outdoor environment.
The prior art is deficient in the lack of an effective conductive paint for one-coat painting which has no restriction in the performance nor in function thereof, can be applied in a wide range in the field of decorative or functional plating, and also can b e applied to the foundation directly. The present invention fulfills this long-standing need and desire in the art.
The present invention was made to solve the problem described above. It is an object of the present invention to develop a conductive paint capable of forming a coating film with extremely high adhesiveness to a plate layer and a method of using the same, and to provide products produced by this conductive paint and this method.
The present invention discloses that a coating film formed with a conductive paint with a conductive whisker mixed therein at a prespecified rate has extemely high adhesiveness with a plate layer. Namely the present invention relates to a plating method for non-conductive products in which a coating film is formed in each required portion with a conductive paint containing solid ingredients at the following ratios; (A) resin vehicle: 20-80 weight %; (B) conductive whisker: 80-20 weight % and electroless plating is executed to a surface of the coating film and to plated non-conductive products obtained by the method. The present invention also relates to a method of plating non-conductive products in which additionally electroplating is executed in some applications.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.
In this invention, non-conductive products are defined as products having a high electrical resistance and practically used as electrically insulating materials including resin, rubber, wood, glass, and cloth.
The resin vehicle used as an ingredient of a coating film used in the conductive paint according to the present invention is a coating film ingredient which has been used in the conventional types of synthetic resin paints.
Examples of an element for forming a coating film as one of the ingredients of the coating film include polyvinyl chloride, polyvinyl acetate, saturated polyester resin, acrylic resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic acid anhydride copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, styrene-butadiene copolymer resin, unsaturated polyester resin, alkyd resin, epoxy resin or a mixture thereof; of these, the vinyl chloride-vinyl acetate-maleic acid anhydride copolymer resin and vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin are preferable, and that simultaneously containing the vinyl chloride-vinyl acetate-maleic acid anhydride copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, or a saturated or unsaturated polyester resin is especially preferable.
Also as a coating film ingredient, in addition to the coating film forming element as described above, pigment and such an agent as a plasticizer, a dispersant, a hardener, and a stabilizer as a supplementary element for a coating film may be used according to the necessity.
Further various types of organic solvent may be used as a supplementary element for forming a coating film, but solvents for synthetic resin paints conventionally used may be used. The solvents include a solvent based on aliphatic hydrocarbons, a solvent based on aromatic hydrocarbons, a solvent based on alcohol, a solvent based on an ester, a solvent based on a ketone, or a mixture thereof.
The conductive whisker used in the present invention is produced by covering a fibrous or needle-shaped monocrystal of a metal oxide or an inorganic salt with a conductive material. A fibrous or needle-shaped monocrystal is often used. Examples of the fibrous or needle-shaped monocrystal of a metal oxide or an inorganic salt include those of sapphire, silicon carbide, potassium titanate, aluminium borate; potassium titanate and aluminium borate are especially preferable.
The conductive whisker with a fiber diameter in a range from 0.1 to 100 xcexcm and a fiber length in a range from 0.5 to 200 xcexcm are preferable, and that with a fiber diameter in a range from 0.3 to 15 xcexcm and a fiber length in a range from 10 to 20 xcexcm is especially preferable.
Material such as silver or tin oxide may be used as the conductive material used for covering the whisker. A quantity of the material used for covering the whisker is not specifically restricted so far as conductivity is given to the whisker.
To advantageously achieve the object of the present invention, however, it is preferable that a surface resistance value of conductive whisker is in a range from 10xc2x0 to 10xe2x88x923 xcexa9/cm (when measured with the Rorester MCP tester from Mitsubishi Yuka K. K). The resin vehicle and conductive whisker can be mixed with each other by solving the resin vehicle in an organic solvent as a supplementary element for forming a coating film and adding the conductive whisker to the solution. The mixing ratio of each component changes according to a type of resin vehicle used in a n application, but generally the resin vehicle is in a range from 20 to 80 weight %, and the conductive whisker is in a range from 80 to 2 0 weight %, and when a percentage of the resin vehicle is less than 20 weight %, the mixture is rather solid and can not easily be handled, and also when a percentage of the resin vehicle is over 80 weight %, the adhesiveness to a plate layer is not sufficient. Preferably a percentage of resin vehicle is in a range from 40 to 60 weight %, and that of the conductive whisker is in a range from 60 to 40 weight %.
Also in the method according to the present invention, a conductive paint shows its effect especially when a coating film is formed directly on a surface of a non-conductive product, but the conductive paint may be applied after a surface of a non-conductive product is subjected to the processing for activating it or for other purpose like in the conventional technology. Adhesiveness of plating executed subsequently can be improved by diluting the conductive paint in an organic solvent, then spraying the solvent containing the conductive paint for coating, and finally drying the coating film. In this case, a thickness of the dried coating film is preferably in a range from 1 to 100 xcexcm, and more preferably in a range from 5 to 25 xcexcm. It is preferable to dry the product at room temperature for 2 to 15 minutes and then to maintain the product at a temperature from 70xc2x0 C. to 90xc2x0 C. for 10 to 60 minutes. In this step, a diameter of each microvoid formed due to the conductive whisker mixed therein advantageously expands because of gasification of a solvent in the coating film or for some other reasons, and adhesiveness of the plate layer increases.
The adhesiveness with a plate layer is remarkably improved especially when a paint produced by blending whisker with an aspect ratio in a range from 10 to 20 and a fiber length of 5 xcexcm or less with a filler for resin vehicle at a blending ratio of 50 to 60 weight %. This mixture is kneaded together with polyisocyanate as a hardening component and a diluent with the viscosity adjusted to 10 seconds with the Ford Cap (FC) #4 (25xc2x0 C.). The mixture is sprayed with a spray gun with a nozzle bore diameter of 1 mm at a spraying pressure of 3 kgf/cm2 so that the dry film thickness will b e 10 xcexcm, left for 10 minutes after setting, dried for 30 minutes under a temperature of 85xc2x0 C. to form a coating film so that micro-voids with a diameter of 3 to 5 xcexcm and a depth of 3 to 5 xcexcm are formed.
In the plating method according to the present invention, it is preferable that a conductive paint is applied to a surface of a non-conductive product, and then the surface is defatted and at the same time activated, and finally electroless plating is executed to the surface with electroplating additionally executed, if necessary.
Various types of metal can be used for electroless plating executed after defatting and activating, but nickel or copper is especially preferable. Also examples of metal used for electroplating executed on the electroless-plated layer include copper, nickel, chrome, tin-nickel alloy, or gold.
When a conductive paint is applied only to sections to be electroplated and then electroplating is executed to the sections, the decorative effect by plating can be improved.
There is no specific restriction over resin constituting a molded product to be processed by the method according to the present invention. Generally the method according to the present invention can be applied to non-conductive products used in vehicles, computer-related apparatuses, and office equipment.